1. Field of the Invention
This invention relates generally to pressure sensors and, more particularly, to a replaceable pressure sensing system for detecting undue pressure applied to a patient's teeth by a laryngoscope.
2. Discussion of the Prior Art
Medical personnel, such as anesthesiologists, use laryngoscopes to gain access to the trachea for inserting tubes during surgery. The tubes are introduced past the glottis and into the trachea or windpipe for permitting the patient to breath and for administering anesthesia.
To insert an endotracheal tube, the patient's head is placed in a neutral or sniffing position and the tip of a laryngoscope blade is inserted into the vallecula. The laryngoscope is held with the index finger and thumb of the left hand and the patient's chin is held with the ring and middle fingers of the same hand. To expose the larynx, the laryngoscope handle and blade are pulled away from the patient at, preferably, a 45.degree. angle. Endotracheal tubes are then passed through the patient's mouth or throat along the laryngoscope blade and into the trachea.
During intubation, the back of the laryngoscope blade, or the laryngoscope flange, frequently contacts the patient's upper front teeth, which are used as a fulcrum. This may result in damage to the patient's teeth. Laryngoscopes having either a pivotally mounted laryngoscope flange or a built-in pressure plate and alarm have been described in the art for alleviating this problem.
U.S. Pat. No. 4,295,465, issued to Racz et al., describes a laryngoscope blade including an elongated base member carrying a projecting flange. The base member has a rear portion, a mid-portion and a tip portion, wherein the rear portion is securely attached to the laryngoscope handle. The flange is pivotally connected by resilient means to the base member and projects upward along the rear and mid-portions such that when the blade is inserted into a patient's mouth, the flange may contact the patient's upper teeth and pivot with respect to the base member. This limits pressure applied to the upper teeth as the flange pivots; however, there is no alarm for indicating when pivoting has ended and excess pressure is being applied. Also, since the rotatable flange is an integral part of the laryngoscope, to utilize this feature a complete laryngoscope must be purchased. This may be cost prohibitive.
U.S. Pat. No. 4,384,570, issued to Roberts, discloses a laryngoscope including a pressure plate positioned on the flange for detecting undue pressure applied to the upper teeth. The plate is electrically connected to a battery and alarm situated in the handle. An electrical signal is transmitted to the alarm for alerting the user thereof to pressure being applied to the plate. The laryngoscope described by Roberts includes a handle section having rigid and movable portions adapted to be pivoted and locked at a desired position. The pressure plate system is not a replaceable sterile unit, separable from the handle configuration. Thus, the pressure sensing system described by Roberts is not independently functioning dental protection which can be supplied as a retrofit device for currently used laryngoscopes. Also, the pressure plate does not cushion the contact with the teeth. A sterile, replaceable laryngoscope pressure sensing system having cushioning properties is needed.
Such a system, must be equally sensitive to pressure applied at any point along the sensor. Devices described in U.S. Pat. No. 3,888,117, issued to Lewis, and U.S. Pat. No. 4,426,884, issued to Polchaninoff are not well suited to this. Each of these patents describe a planar electrical conductor held in spaced relation to a plurality of spaced electrical contacts. Pressure applied to the planar conductor relative to the contacts urges the two together. Using these devices to detect pressure applied by teeth may give inconsistent and unreliable results since, on some occasions, the teeth may be situated directly over an electrical contact and on others, the teeth may be between contacts.
Sensors for detecting pressure with equal sensitivity at any point along the length thereof may be of the linear membrane variety or may use piezoelectric film, such as the film used in U.S. Pat. No. 4,488,873, issued to Bloomfield et al. The '873 patent describes a dental impression strip prepared from a piezoelectric film coated with conventional deformable wax impression material. The film and wax assembly is folded to provide information about the forces exerted during occlusal analysis. The film is KYNAR.RTM. piezofilm, a polyvinylidene fluoride product of the Pennwalt Corporation of Philadelphia, Pa., which may be configured for use in the present invention.